# Testing and calibration of hygrometers



## Demented (Nov 7, 2006)

Testing hygrometer accuracy can be done in two common ways:

1. Wrap a damp cloth on the back of the hygrometer for 6 hours. The indicator should then read approx. 95%. If it reads lower or is off scale completely, adjust the indicator to read 95%.

2. Place a teaspoon or so of salt in the shallow container and add a few drops of water - just enough to get it wet. Remember, you don't want a salt water solution, just damp salt. Place the shallow container in a baggie along with the hygrometer. (Make sure the salt does not get on the hygrometer, this may damage it). Seal the baggie with some air trapped inside and let it sit for 6 to 8 hours. Check the hygrometer reading without opening up the baggie. It should read 75%. If not, remove the instrument from the baggie and adjust the reading to 75% with a small screwdriver.

To maintain accuracy of the instrument, it is advisable to recalibrate every six months.

Science Company

The Mason type Wet & Dry Bulb Hygrometer is the most accurate method known to obtain humidity readings. These instruments are on the large side, 10"x 4" and larger, not practical for even the largest of desktop humidors, but for 100% accuracy in a display or other large cabinet style humidor nothing is better. Prices start around $40.00.

School Masters

Measuring humidity is not as precise as measuring temperature. Even hygrometers for professional laboratory use are typical only guaranteed to be accurate by ±2.

Types of hygrometers,

Analog hygrometers with a metal spring (those which come with many humidors), theoretically are accurate at a given temperature and within a narrow range of the scale. A metal coil, can not and doesn't react well enough to humidity to be of any use where the preservation of cigars is concerned.

Natural hair hygrometers, are more accurate, but a high level of maintenance is required to maintain the accuracy, these hygrometers are expensive and of limited use in a humidor.

Synthetic hair hygrometers are approximately as accurate as natural hair hygrometers. However they do not require any maintenance on the part of the user. Therefore, they should be the first choice for use in humidors.

Digital hygrometer, which allow for easier readability are not necessarily more accurate than analog hygrometers.

Hygrometers analog or digital

Shocks during transport or long storage in a dry environment may case cause inaccuracy in analog hygrometers, they should be tested and calibrated.

In the case where it's been out of service for a time. Wrapping the instrument in a wet towel for 6-8 hours, will in most cases be enough to hydrate the element. After this the hygrometer should indicate a relative humidity 95%. If not adjust it and repeat the procedure.

Boveda Humidification Packets can also be used to test and calibrate hygrometers.

Analog or synthetic-hair hygrometers work using a strand of humidity
sensitive polymer to mechanically move the indicator.

Digital or capacitance-resistance hygrometers work by measuring current flow across a semi-conductor.

Dmntd


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## mhillsing23 (Apr 18, 2006)

Known info, but a good summary.


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## raodwarior (Oct 28, 2006)

Best method is to get a Boveda calibration bag and take all the guess work out of it.


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## Demented (Nov 7, 2006)

Hygrometers built into humidors.

Unless the hygrometer is accessible from the back and is adjustable, there not much you can do other then test it for accuracy.

Needed for testing a built in hygrometer; Ziploc freezer bag, new sponge, distilled water.

Mark the bag and cut a hole in it, so when put in the humidor the sponge will be against the side of the humidor where the holes drilled for the hygrometer. Wet the sponge with distilled water and wedge it against the back of the hygrometer, close the humidor and leave it for 6 hours, before checking the hygrometer.

It should read around 95%, if not, adjust the hygrometer if possible, make a note of how much it’s off or purchase a quality instrument.

No guess work about it.

Dmntd


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## Rploaded (Nov 7, 2006)

Demented said:


> Measuring humidity is not as precise as measuring temperature. Even hygrometers for professional laboratory use are typical only guaranteed to be accurate by ±2%


If you search online for Laboratory clean rooms and climate control rooms, they can get it down to 1/10th of 1%.

But at the point you are spending millions of dollars but laboratory equipment can be very accurate.

I read at one place you have to wear full breathing gear to prvent your exhalations from disrupting the control.


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## Demented (Nov 7, 2006)

Rploaded said:


> If you search...


Thank You for your input.

I'm sure it will prove very useful in the pursuit of this hobby and the preservation of cigars.

Dmntd


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## Puffin Fresh (Nov 1, 2006)

Thanks for the advice mang.


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## bama (Jan 24, 2007)

I have yet to find a way to manually adjust the analog hygrometers I have. I keep reading about using a scredriver to adjust, but I have not found any possible way to do that. Is it just the type of hygros I have, or am I missing something here?


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## icehog3 (Feb 20, 2005)

bama said:


> I have yet to find a way to manually adjust the analog hygrometers I have. I keep reading about using a scredriver to adjust, but I have not found any possible way to do that. Is it just the type of hygros I have, or am I missing something here?


Analog hygrometers are notoriously inaccurate. Even with manual adjustment, the ones I had early in my humidor days seemed to fall off the accurate RH in short order. Buying a digital hygrometer and using the salt or Boveda test to gauge its accuracy is the best surefire method to rest easy. :2


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## DudeGroovin (Oct 16, 2006)

I'm considering a humidor with an externally readable Analog Hygrometer. The big analog hygros look so snazzy on some humidors. What to do about the inaccuracy? Adjust it to read my desired relative humidity, use a drop of cyanoacrylic glue to permanently fix the needle on that reading, and then put an accurate and calibrated digital hygrometer inside the humidor.

Will look nice on the outside, and work right on the inside.


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## icehog3 (Feb 20, 2005)

DudeGroovin said:


> I'm considering a humidor with an externally readable Analog Hygrometer. The big analog hygros look so snazzy on some humidors. What to do about the inaccuracy? Adjust it to read my desired relative humidity, use a drop of cyanoacrylic glue to permanently fix the needle on that reading, and then put an accurate and calibrated digital hygrometer inside the humidor.
> 
> Will look nice on the outside, and work right on the inside.


They are attractive, I'll give you that....sounds like a plan.


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